Measuring relative angular positional displacement and the angular range of motion for body segments and articulating joints of the human skeleton is of value in the medical and rehabilitation fields. For example, with reference to the human spine, the primary spinal range-of-motion measurements, postural zero (straight up) to full flexion, postural zero to hyper-extension, postural zero to full left lateral bend, and postural zero to full right lateral bend, are used as part of the diagnosis of various spine and back-muscle disorders and diseases. As a patient engages in physical therapy or receives other treatment, the angular range of motion should increase, resulting in a changed measured value. However, prior instruments for measuring relative angular position and angular range of motion have not been found to be effective or accurate.
In the past, doctors, clinicians and other medical professionals and paraprofessionals have measured the relative angular position and the angular range of motion for body segments and articulating joints of the human skeleton using mechanical inclinometers. These prior instruments were designed for use by plumbers and carpenters and therefore lack necessary features for use on the human skeleton. Such instruments are accurate only within plus or minus 1.degree. over a 360.degree. range, an accuracy which is not sufficient, for example, for the measurements made of the angular range of motion of the human spine, where an accuracy within plus or minus 0.5.degree. is desired. Mechanical inclinometers are often large and bulky and cannot be easily stabilized against the body segment or articulating joint, making it impossible to duplicate test conditions for two different measurements. Also, such instruments, because they do not have computational ability built into them, lack the ability to compute differential angles between two body segments. Further, such instruments are unsuitable for measurements in the lateral plane, as when a person bends from side to side at the waist.
There has been a need for an easy to use, hand-held device which avoids the above-described problems.